The present invention relates to a process for controlling the power supply of an electrostatic filter, and in particular, to a power supply including an indirect converter (e.g. a three phase to one phase converter) being equipped with a measuring and control unit, and a high-voltage transformer.
Power supply devices of the above-mentioned type are disclosed, for example, by the German Published Patent Application 35 22 569. A major disadvantage associated with the previously known control process is that, to determine the states of the secondary-circuit, the filter current and the filter voltage in the secondary circuit (i.e., on the high-voltage side of the transformer) must be measured. Devices for measuring current and voltage under high voltage conditions are expensive and susceptible to faults. In addition, extensive shielding and insulating measures must be taken to ensure safety for service personnel. On the other hand, determining the states of the secondary-circuit is absolutely necessary since the electrostatic filter is supposed to be controlled as optimally as possible and, to accomplish this optimal control, the setpoint values, for example those for the intermediate-circuit current, must be constantly adapted.
Due to the above-described problems with measuring voltage and current under high-voltage conditions, up until now the setpoint selection for values (e.g., intermediate-circuit current, pulse repetition rate or pulse duration) was made by measuring the characteristic filter curve. Using this measurement, new setpoint values were then specified manually based on the experience of the service personnel.
However, when using the characteristic filter curve for setpoint selection, the reliability and accuracy of the selection depends on the experience and attentiveness of service personnel which leads to high labor costs.
As mentioned earlier, the electrostatic filter must be operated optimally, particularly due to strengthened environmental laws. Since the breakdown (i.e., disruptive discharge) voltage of the filter changes during operation, the setpoint values must always be redefined and adapted to enable an optimal operation. Even trained personnel cannot constantly adapt the setpoint values because of the speed at which the breakdown voltage changes.
A first object of the present invention is to provide a method for setpoint selection in which measuring voltage and current in the secondary circuit under high-voltage conditions is not required. Another object of the present invention is to accelerate and automate the setpoint selection so that the electrostatic filter may be optimally controlled and so environmental protection regulations may be met. In addition, for reasons of economic efficiency, retrofiting existing installations with the control process according to the invention should be possible. Furthermore, the automation in setpoint selection should reduce personnel costs.